Local anesthetics, when injected as a solution in normal saline, in general cause pain. Wightman, M. A. et al., Anesthesiology 45:687-689 (1976). In addition, all topical anesthetic preparations sting when applied to the cornea. Some anesthetics were shown to cause less pain than others. These authors provided a method to measure the pain of local anesthetic injection. They reported the first modern painless local anesthetic, bacteriostatic saline, which comprises 0.9% benzyl alcohol in normal saline. They reported bacteriostatic saline painlessly produces mild skin anesthesia after intradermal injection. However, the anesthesia was not profound and lasted for only 10-15 minutes. This was long enough to start an I.V., but not long enough to keep the site from hurting. However, use of solutions containing benzyl alcohol are not preferred because benzyl alcohol is cytotoxic and has been cited as playing a possible role in flaccid paraparesis following obstetric epidural anesthesia. Douglas, C. et al., Anesth. Analg. 56:219-22 (1977). Other disadvantages of benzyl alcohol containing solutions are that they sting when applied to the cornea and are ineffective as a topical anesthetic.
Other workers have reported that the warming of local anesthetic agents prior to administration helps to decrease the discomfort associated with injection. Bloom, L. H. et al., Opthalmic. Surg. 15:603 (1984). Traditional methods of decreasing the pain of the injection of local anesthetics include hypnosis (suggestion) and sedatives (amnesia producing drugs). Still other workers have reported application of a local anesthetic cream to decrease the pain of injection. Hallen, B. et al., Anesthesia 39:969-972 (1984); Hallen et al., Anesthesiology 57:340-342 (1982).
The pain of injection around and behind the eye can cause cardiac arrest, induce angina, incite asthma, and cause nausea and vomiting. The use of sedatives to ward off these problems has played a key role in anesthesia safety. However, stimuli from injection can cause an untoward response despite high doses of sedatives. In addition, sedatives can have undesirable side effects once the pain of injection is gone. These include disorientation and difficulty in establishing the success of a nerve block. Residual sedation can interfere with the safe ambulation of the elderly. Thus, patient safety is best served by avoiding pain. In addition, patients will be better served if the pain of injection of local anesthetics is reduced.
Thus, a need exists for compositions and methods for administering local anesthetics which do not cause pain. In addition, a need exists for solutions which may be used to irrigate wounds, abrasions, lacerations, and burns without pain.